I'm in a village halfway between Liskeard and Callington and I used to work at the secondary schools at Liskeard, Looe and Callington. All fairly okay small towns. I don't think Liskeard is a shit-hole...it has its fair share of drunken louts on a late Friday/Saturday night but other than that the place is fairly sedate with a low crime rate. (I grew up on a council estate in West Yorkshire with high levels of poverty and crime). I've lived here for ten years.
I agree that the local children's centres are good for parent and baby/toddler groups and the libraries are also good (I work at Callington library). We run Bounce and Rhyme (as does Liskeard library) and Booklets storytime. The children's centres all run the same groups across the area pretty much, with only slight variations. I'll post a link to Liskeard Children Centre's brochure below:
www.dobwalls.cornwall.sch.uk/parents%20resources/Lisk%20What%27s%20on%20Guide.pdf
There is also Lux Park Leisure centre which has soft play, Sterts theatre has (or used to have) Monkey Music and there are often parent/baby groups run in the surrounding villages especially if it has a primary school. We used to have Baby signing run by a Liskeard mum I know but I'm not sure if she's running it at the moment.
I have two sets of twins, aged five and 13 months and I have been along to many a group in the past few years!
We also have a booklet printed by the council that comes out every half-term with various activities running during school holidays and a magazine called Blackbird Pie as well as Primary Times which list local activities/venues for babies - school aged children.
It is also worth looking at the council's FIS (Family Information Service) page:
cornwall.childrensservicedirectory.org.uk/
So there is plenty to do really :) And we're not all that far from Plymouth either where there is a huge soft-play place and an aquarium. The Eden Project is just under an hour away near St Blazey, and of course there are lots of other places in the county to visit - beaches, moors, parks etc etc etc.